Participants ≥ 2 years of age with PROS with documented somatic PIK3CA mutations or Proteus syndrome with documented somatic AKT1 mutations were enrolled to receive oral miransertib at a starting dose of 15 mg/m2 every day for the first 3 cycles (1 cycle = 28 days) and miransertib 25 mg/m2 every day thereafter, provided no clinically significant drug-related toxicities were observed. Here, AKT1 is linked to Proteus syndrome.